This invention relates to novel reactive systems consisting of a special polyisocyanate component and a reactive component for this polyisocyanate component and of auxiliaries and additives. This invention further relates to a process for the preparation of polyurethane plastics containing isocyanurate groups using these reactive systems.
The preparation of plastics containing isocyanurate groups has long been known and in various forms is carried out on an industrial scale. For example, German Offenlegungsschrift 2,534,247 describes a process for the preparation of moldings based on isocyanurate-modified polyurethanes using strongly basic compounds, such as alkali acetates or alkali phenolates, as trimerization catalysts. Hardening times of 0.75 to 2 minutes can be obtained with these catalysts. This process, however, cannot be used for longer hardening times (that is, for the longer pot lives of the reaction mixtures which are often required in practice) because the basic catalysts must then be used in very small quantities. Consequently, acidic impurities, which can be present in the starting materials or additives, can have a completely uncontrollable effect on the time taken by the hardening reaction by neutralizing the catalyst. Reproducible processing of the starting materials is then no longer possible.
Although the Mannich bases recommended as trimerization catalysts, for example, in German Offenlegungsschrift 1,809,391 provide for longer pot lives, such compounds suffer the disadvantage of very slow and often incomplete final hardening, resulting in poorer thermal properties of the resulting plastics.
The object of the present invention is to provide new reactive systems which react to form high-quality polyurethanes containing isocyanurate groups but which are not attended by the disadvantages of previously known systems. The desired reactive systems should have a sufficiently long pot life for practical requirements at room temperature or only moderately elevated temperature, coupled with short hardening times at elevated temperatures. This object is achieved by the reactive systems of the invention, which are described in detail hereinafter, when used in the process of the invention for preparing isocyanurate-modified polyurethane plastics.